Method of producing coke



Dea/7, 1937. M. B. COOKE ET AL METHQD OF PRODUCING COKE Filed April 20,l9 34 v LUWCUBQOU kw ATTQRNE Patented Dec. 7, 1937 UNITED STATES 4PATLNT,o1-"F1011,

n Mllrnon or rnoDUclNc come Application April zo, 19er, serial No.'521,496 2 claims.' (cl. 2oz- 16) Our invention relates to the art ofdistillation and more particularly to the distillation of asphaltums,asphaltic residuums andheavy petroleum residues for the production ofsolid, dry coke. The production of coke from the standpoint of petroleumrefining may be generally classified under two main headings; rst, cokeproduced from shell st-ill distillation of reduced crude and, second,coke produced as a by-product of a cracking operation.

yEach of .these processes embraces a particular field. The production ofcoke from shell still distillation of heavy residuums is a secondaryfeature arising from the primary purpose which is to recover thegasoline and heavier products from the residue. The formation of coke inlarge quantitles is objectionable from the standpoint of cicientoperation of a shell still. For example, a heavy oil residuum of 5 A. P.I. gravity must be distilled at temperatures ranging between 920 F.. to940 F. to recover the lighter fractions contained therein. A residuum ofthis gravity will coke at temperaturesranging between 800 F. to

' 875 F. if distilled as a substantially stagnant pool. The inefficiencyof the process because of carbon deposition renders this method ofdistillation quite uneconomical.

The non-residue cracking of gas oil and heavier distillates for theproduction of gasoline is accompanied by the production-of coke. Suchcoke is generally of low market value and 'unsatisfactory because ofwetness from retained volatiles which, when the c oke is burned, producesoot and foul the furnace. The coke crumbles readily, frequentlyexplodes because of occluded oil, and is not readily salable fordomestic `and industrial consumption. Very seldom-is this coke directlysuitable for metallurgical purposes.

It is an object of our invention, therefore, to provide a process forproducing a solid dry coke from asphalt or a heavy petroleum residuum,recovered from any previous distillation or cracking operation, whichwill be suitable for domestic `or industrial consumption. y

It is a further object of your invention to provide a process in which aheat carrying medium is utilized-to produce a solid dry coke fromasphalt or a heavy petroleum residuum recovered from anypreviousdistillation or cracking operation.

It is a still further object of our invention to 'provide a combinedcoking and distillation process which will produce a solid dry. coke andxed gas and secure a 'substantial recovery of hydrocarbon, distillateoli, substantially a gas oil boiling elevation with parts in section ofone form of aptower or from any other suitable source, is heated range,`from asphalt or a heavy petroleum residuum recovered from any previousdistillation or cracking operation.

It is another object of our invention to provide a coking processutilizing a heat carrying medium in which the volatile content of thecoke Produced is controlled by the time temperature relationship of heatcarrying mediumto liquid established in the coking chamber.

Another object of our invention is to provide a coking process in whichthose heavy fractions notinitially coked are continuously recycled -tosecure complete reduction to and a maximum yield of coke from theinitial charge.

Another object of our invention is to provide al coking process in whichthe composition of the heat carrying medium recovered 1in the processmay be controlled to obtain the most suitable reactant for the cokingoperation.

Other and further objects of our invention will appear from thefollowing specification and claims.

The accompanying drawing, which forms part of the instant specicationand is to be read in conjunction therewith, is a schematic showing inparatus capable of carrying out the process of our invention.

In general, we subject asphaltic residuum or heavy petroleum oil tofractionation as a result ofv which a bottom fraction, ofconstantfqu'a'lity with respect to gravity, distillation-and boilingrange, and lighter distillatesare'formed. The bottom fraction is heatedunder conditions which will prevent the formation and deposition ofcarbon in the heating element and will substantially avoid cracking. Aheat carrying medium which may be a gas or light distillate, recovered,for example, from the overhead products of the fractionating to atemperature above that of the heated fractionI to be cokedand physicallymingled with the .heated liquid fraction in a coking chamber. As

a result of the heatinterchange between the heated liquid fraction andthe heat carrying inedium, a carbonizing of the petroleum compounds iseffected with a resultant production of coke, gas, and volatiles whichlatter are mainly of 'gasoil boiling range. The volatiles and gas areremoved from the coking drum and returned to the fractionating towerwhere by fractionation the heaviest ends are removed and recycled forcomplete coking, and the lighter ends recovered for use as a heatcarrying medium in the system. As a result of the operation of ourprocess We are enabled to produce not only a maximum yield of solid drycoke from an initial charge, but also to recover a considerable amountof Vdistillates of gas oil character.

Referring now more particularly to the drawing, the petroleum to beprocessed is led from a source (not shown) through a line l having apump 2 to the lower section of a two section fractionating towerindicated generally as 3. The heaviest f-raction which accumulates inthe bottom of this tower is pumped through the line 0 having a pump 5 toa convection section G of the furnace setting l. This convection section6 is connected by means of a line 8 to the tubes of a radiant heatingsection 9' of the furnace from which a line IU leads to the feed line 35of a heat carrying medium. From the top of the fractionating tower 3 aline l l leads to a vapor condenser l2 which is provided with coolingliquid inlet means I3 and outlet means lll. This condenser l2 isconnected by means of aline l5 with a separator I3 from the top of whicha line il', provided with a bleed-olf line lB8, is connected to theintake side of a compressor I9. The outlet side of this compressor isconnected by means of a line 20 to the bottom of a combined strippingand gas enriching tower 2i provided with baille means 22 and traysindicated generally as 22. The gas reduces the partial pressure and actsas a stripping medium. From a suitable section of the fractionatingtower 9 a line 23 provided with a ,pump 29 leads to the upper tray ofthe stripping section in the tower 2l. A withdrawal line 25 from thebottom of; the tower 2 l, passes through a cooler 2l provided withliquid inlet and outlet means 29 and 29, respectively, to a storage tank(not shown). A branch line 2li having suitable valves passes through theheat exchanger 30, and cooler 30a provided with cooling liquid inlet andoutlet means 32 and 33', respectively, to a suitable tray of thefractionating tower 3.

l The heat exchanger 30 may be bypassed by means of a line 26' having avalve. The separator I3 is provided with a withdrawal line 39 having apump 40 for the removal of light distillate collected in the separatorI6 and for delivering it to storage or for further processing. A line ilconnects the withdrawal line 39 with the top of the fractionating tower3 for the return of reflux thereto. From any suitable point on the lineM, a line lla having a valve 4| b leads through the heat exchanger 30 tothe trays in the upper part of the gas enriching section of the tower2l.

Connected to the top of the tower 2i is the heat carrying medium feedline 3l which leads to the tubes of the economizer convection section 32of the furnace setting l'. This convection section is connected bymeansof the line 33 to the tubes 39 of a radiant heating section of thefurnace. The outlet from these tubes is connected by means of a line 35with a coking chamber 36. This line 35 may be manifolded and connected'to a plurality of coking chambers although We have shown but one forthe sake of simplicity. In the event that a plurality of these chambersis used, it becomes possible to utilize any one for coking while anotheris being cleaned of the coke which may already have accumulated thereinfrom a previous coking operation. The upper part of the coking drum 36is connected to the bottom section of the f ractionating tower 3 bymeans of a line 3l. The upper and lower sections of the fractionatingtower are connected by means of a large vapor passage 38 and liquidreturn line 38 which serves to return part of the condensate from theupper portion of the tower to the lower portion to knock back heavy endscarried over by the vapors from the lower tothe upper portion of thetower. A line 40 returns uncoked residuum for recycling.

An example of the operation of our invention is as follows: Asphalt,asphaltic residuums or heavy petroleum residue is charged by means ofthe pump 2 through the line l to the fractionating tower 3 wherein theliquid is partially vaporized, the vapors rising upward through thetower in which fractional condensates collect on the various trays. Theheavy liquid fraction which collects in the bottom of the tower, andwhich maybe, for example, at a temperature ranging between 600 F. to 750F., and which, under the pressure and temperature conditions maintainedin this portion of the tower will be kept free from light ends, ispumped through the line 0 by means of the pump 5 through the convectionsection 6, connecting line 8 and radiantly heated section 9 of thefurnace setting l. The velocity of the liquidthrough the tubes of theseheating sections is such as to prevent the forma- Y tion and depositionof carbon and substantially avoid cracking. The heated liquid oil whichhas been raised to a temperature between 800 F. 875 F. or a temperatureas high as possible without deposition of coke in the tubes, is chargedthrough the line I0 to the line 35 in which it is contacted by a heatcarrying medium which has been recovered from the fractionating systemor other suitable source and enriched or treated to secure the desiredconstituencyl in a manner which will be more fully describedhereinafter.

As a result of the physical mingling of the heat carrying medium andliquid oil in the coking drum wherein the mixture will be, for example,at a temperature ranging between 900-l000 F. depending on the characterof the oil to be converted to coke and the constituency of the heatcarrying medium, a carbonizing or coking of the heavy liquid petroleumwill be effected with the simultaneous evolution of lighterhydrocarbons, a minor portion of gas and gasoline and a major portion ofgas oil boiling range fraction. It is also to be observed that as theresult of the physical mingling of the liquid and heat carrying mediumat the selected temperature, a dry solid coke is produced which willhave a minimum amount of occluded oil. When a suitable amount of cokehas accumulated within the vessel 36 another vessel of the battery maybe selected to continue the coking and the solid coke in the firstvessel may be removed by any of the means well known in the art.Satisfactory operation of a coking vessel of this type is secured bymeans of the temperature level and the temperature difference in inletand outlet held in this chamber. A further means of securing eicientfunctioning of this drum, that is, the attaining of a maximum productionof coke per pass while leaving a minimum amount of heavy fractions to berecycled as liquid, is by the regulation of the composition. Forexample, at a given composition of the liquid charge and the heatcarrying medium, syphoning or other irregularities in the drum willoccur under given `temperature conditions. Elimination of this improperfunctioning of this drum may be obtained by fixing the inlet temperatureand varying the outlet temperature of the drum, to establish a fixedtemperature difference between inlet and outlet, or by maintaining thesame outlet temperature and varying the inlet temperature to secure afixed temperature difference beatomen tween inlet and outlet. The oilvapor and gas leaving the coking drum 3B vwhich are, for example, at atemperature ranging from 875 to 950 F. are delivered through the line 3lto the bottom of the Afractionating tower 3 for separation orfractionation. The vapor inlet to the bottom section of thefractionating tower is submerged below the liquid level maintained inthis section for the purpose of immediate temperature reduction of thehot vapors and for securing stripping action upon the liquid containedin the bottom of the tower. The ascending vapors are further cooled andfractionated when passing through the trays above, counter-current tothe incoming fresh feed from the line i and the supplementary refluxwithdrawn from the bottom of the upper section of the tower through theline 33. After this process the vapors rise upward through the largevapor passage 38 into the upper section of the fractionating tower 3.Here a separation is made between thelight and heavy ends, which latterare mainly gas oil boiling range constituents which are withdrawnthrough line 23 at a temperature ranging from approximately 500 to 550F. The lighter ends consisting of a light distillate and gas arewithdrawn from the top of the tower through line I I to be recovered andmostly recycled in the system as the heat carrying medium.

Returning now to the fractionating tower, the light distillate and gaswhich under the temperature and pressure conditions existing in thefractionating tower have not ybeen condensed on the various trays areremoved through the line I I and are passed through the vapor condenseri2 wherein the light distillate is liqueed and the degreeof condensationis controlled by the condenser outlet temperature to secure a gas ofsuch leanness as will function most eiectively as a gas oil strippingagent later in the process. The cooling of this vapor condenser iseffected by water which enters through e line I3 and after .circulationis removed through the line I4. The

distillate and gases are removed from the vapor 'condenser through theline I5 and passed into the separator I6 from which the light distillateis removed through the line 39 by means. of the pump 40 an a portiondelivered to storage'. The

other porti n of light -distillate is returned in part" as reux to thetop of the fractionating ,bwer 3 through the line 4I and in Dart-usedforjcntrolling the constituency ofith' heat carrying medium inthestripping tower 2|. The gas or uncondensed fraction is taken o overheadthrough the line I1 tothe intake side of the compressor I9. The amountin excess of the fraction desired as a heat carrying medium iscontinuously removed from the line I1 through the line I8. The'compressor I9 will deliver the gas at a pres- 'sure for example of-50#-100# per square inch to the bottom of the tower 2I.

Gas oil at a temperature of around 50o-550 F. removed from thefractionating tower 3 by means of pump 24 and the line 23 is charged toa section below the uppermost or enrichment trays of the tower 2l l'I'hegas delivered to the bottom of the tower rises upward and comes intointimate contact with the liquid gas oil descending over the bafliesection of the tower.V The gas serves to strip from the gas oil thenecessary fractions so that the gas oil will meet the necessaryspecifications with respect to ash point. The gas oil is removed fromthe bottom of the tower 2I through the line 25 and is cooled in thecooler 21 to which cooling u liquid is fed through the line 28 andremoved Vheat exchanger 30. It will be observed that through the line29; The gas oil after cooling may then be delivered to storage. Theportion of the gas oil in excess of the net gas oil producedl which maybe at a temperature ranging from 400 to 450 F. is diverted through theline 26, heat exchanger 30, and cooler 30a and delivered to a suitabletray in the fractionating tower 3 to serve as intermediate Areux. Thecooler 30a is provided with suitable cooling liquid inlet and outletmeans 32 and 33 respectively. A certain portion of the light distillateflowing through the line di from the separator it is diverted throughthe line ila having a valve Mb and passed in heat interchangerelationship in the exchanger 30 with the gas oil delivered thereto bymeans of the line 26. The heated light distillate is delivered from theexchanger 30 to the tower 2l at a point above the top tray of the gasenriching section of this tower. By this means we are enabled to providefor an enrichment of the heat carrying medium in the upper part of thetower 2i before delivery to the furnace l. The temperature of the lightdistillate delivered to the upper part of the tower 2l may be controlledby suitable manipulation of the valves in lines 26 and 26'; whoseadjustment/will permit any desired amount of gas oil to iiow through themeans of the' vapor condenser I2 we have be able to control the leannessof the gas delivered to the stripping section of the tower 2l to securethe most eiective stripping of the descending gas 'oil and by thetemperature control of the light livered under pressure through the line3i to the economizer convection section 3d of the furnace-l. These gasesare raised in the furnace to a temperature between 1100 and 1200 F., areremoved through the line 35, an contacted with the heated liquid oilfrom th line I0 to the coking drum 36. v Y

It is to be understood that the recital of temperatures and pressures inconnection with the various steps of the process is by way of exampleonly since the ex'act gures must be selected in accordance with thecharacter of the petroleum being processedl and the constituency of theheat carrying medium.

' It is to be observed that we have accomplished the objects of ourinvention and have provided a process which will produce a dry coke forany grade of charging stock and secure recovery of a maximum amount ofdistillate of substantially a gas oil boiling range ,gas and a minoramount of light distillate from asphalt or a heavy petroleum residuum. l

It will be understood that certain features, combinations and operationsare of utility and may be employed without reference to other featuresand sub-combinations. This is contemplated by and is within the scope ofour claims. It is further obvious that various changes may be made indetails within the scope of our claims without-departing from the spirit'of our invention. It is, therefore, to be understood that our inventionis not to be limited to the specic I leum oils, comprising the steps ofpassing the oil to a fractionating zone, withdrawing the residuetherefrom, passing the 'residue to a heating zone and there heating theresidue, passing the heated residue to a carbonizing zone, removing theuncondensed mixture of hydrocarbon vaporsand gases from thefractionating zone, cooling the mixture suciently to condense thedistillate therefrom and leave a substantially gasoline free lean gas,passing a stream of the lean gas to a stripping zone, withdrawing a sidestream from the fractionating zone and passing it to the strippingzona-intimately contacting the lean gas in the stripping zone with theside stream and withdrawing the stripped side stream from the strippingzone, withdrawing from the stripping zone the mixture oi' lean gas andproducts stripped from the side stream, heating the gaseous mixture,physically mingling the heated gas with the heated residue passing tothe carbonizing zone, effecting carbonizing of the condensate by theheated gas'under time temperature conditions productive mainly ofhydrocarbon vapors and a solid dry coke, and returning the vapors to thefractionating zone.

2. A process for coking asphaltums, asphaltic residuums or heavyhydrocarbon oils comprising the steps of separating the uncondensed gasvapor mixture withdrawn from a fractionating zone into a distillate anda substantially gasoline free cool lean gas, passing the cool lean gasinto a stripping zone, intimately contacting the gas therein with adownfiowing stream of relatively hot liquid withdrawn from thefractionatlng zone whereby the gas is heated land enriched with lighthydrocarbons undesirable in the stripped product, withdrawing thestripped liquid from thev stripping zone,. heating a relatively heavyhydrocarbon oil, separately heating a stream of enriched gas withdrawnfrom the stripping zone to a temperature sulcient to ensure coking ofthe heated oil, intimately physically commingling the heated oil andgas, causing carbonizing of the oil and decomposition of the heated gasto take place under time temperature conditions productive mainly ofvhydrocarbon vapors and a solid dry coke, and returning the vapors tothe fractionating zone.

